A central theme in this PPG is the genetically engineered mouse. This Core is the Gene-Targeted Mouse Facility, located at The Rockefeller University. The facility will provide the gene=targeted mice that will be used in each of the subprojects. Most of these mice have already been developed by Dr. Mombaerts in his laboratory at The Rockefeller University. New strains will be developed and deposited in this core. Because duplicating these lines of mice at other institutions is costly and because quality control must be stringent, we have elected to utilize a single facility through which mice will be distribute to each of the groups. Centralized breeding of the gene-targeted mice will not pose a hurdle because of the geographical proximity of the various laboratories.